Answers

On the map are icons thatlook like the assassin logo. go to one of them and it will either be a pigeon coop or a tower. There is a coop about halfway up your homebase just go there click 'B' and then go down and select contracts

First you need to recruit guild members. This can be done by assisting citizens being assaulted by Borgia guards (these appear as diamond-shaped icons on the map).

You then need to find a Pigeon Coop or Assassin Tower. These are represented by white colored Assassin's Guild symbols on the map. Get close and press 'B' to interact.

You can also send recruits on missions by interacting with a map sitting on a table in Ezio's hideout. Simply enter the hideout and walk down the stairs, it is just on the right; again get close and press 'B'.

Once you've done this, you should see a menu with four options. Choose 'Assassins' to view your recruits or level them up after they gain experience. Choose 'Contracts' to send your recruits out on missions to gain experience for them and monetary rewards for you. Note that multiple recruits can be sent on the same mission. Once you have one or two high-level recruits, you can level the rest easily by sending them out on 3- or 4-star missions with your newbies- all experience is split equally.